package javaLearning.Steam流式;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author : K k
 * @date : 22:58 2020/9/15
 */
public class Apple {
    private Integer id;
    private String name;
    private BigDecimal money;
    private Integer num;

    public Apple(Integer id, String name, BigDecimal money, Integer num) {
        this.id = id;
        this.name = name;
        this.money = money;
        this.num = num;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public BigDecimal getMoney() {
        return money;
    }

    public void setMoney(BigDecimal money) {
        this.money = money;
    }

    public Integer getNum() {
        return num;
    }

    public void setNum(Integer num) {
        this.num = num;
    }

    @Override
    public String toString() {
        return "Apple{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", money=" + money +
                ", num=" + num +
                '}';
    }

    public static void main(String[] args) {
        List<Apple> appleList = new ArrayList<>();//存放apple对象集合

        Apple apple1 =  new Apple(1,"苹果1",new BigDecimal("3.25"),10);
        Apple apple12 = new Apple(1,"苹果2",new BigDecimal("1.35"),20);
        Apple apple2 =  new Apple(2,"香蕉",new BigDecimal("2.89"),30);
        Apple apple3 =  new Apple(3,"荔枝",new BigDecimal("9.99"),40);

        appleList.add(apple1);
        appleList.add(apple12);
        appleList.add(apple2);
        appleList.add(apple3);

        //List 以ID分组 Map<Integer,List<Apple>>
        Map<Integer, List<Apple>> groupBy = appleList.stream().collect(Collectors.groupingBy(Apple::getId));
        //System.err.println("groupBy:"+groupBy);

        /**
         * List -> Map
         * 需要注意的是：
         * toMap 如果集合对象有重复的key，会报错Duplicate key ....
         *  apple1,apple12的id都为1。
         *  可以用 (k1,k2)->k1 来设置，如果有重复的key,则保留key1,舍弃key2
         *  Key:id value:apple对象
         */
        Map<Integer, Apple> appleMap = appleList.stream().collect(Collectors.toMap(Apple::getId, a -> a,(k1,k2)->k1));
        //System.out.println(appleMap);

        //过滤出符合条件的数据
        List<Apple> filterList = appleList.stream().filter(a -> a.getName().equals("香蕉")).collect(Collectors.toList());
        System.err.println("filterList:"+filterList);

        //计算 总金额
        BigDecimal totalMoney = appleList.stream().map(Apple::getMoney).reduce(BigDecimal.ZERO, BigDecimal::add);
        //System.err.println("totalMoney:"+totalMoney);  //totalMoney:17.48

    }

}
